How does intake of common salt cause heart disease?

Intake of common salt is primarily related to the development of hypertension 9HT, which is a major risk factor for the development of heart attack called Coronary Heart Disease(CHD).

For many diseases, the disease agent is still unidentified, e.g., CHD, cancer, peptic ulcer, mental illness, etc.

In these conditions, the cause of the disease is generally discussed in terms of risk factors. Risk factors are often suggestive, but absolute proof of cause and effect between a risk factor and disease is usually lacking.

The effect of risk factors is multiplicative rather than additive; thus, people with combination of risk factors (e.g., smoking, HT, diabetes etc.,) have the greater risk of developing CHD.

It is important to distinguish between relative risk (the proportional increase in risk) and the absolute risk (the actual chance of an event).

Thus, a person of 35 with high cholesterol level who smokes 40 cigarettes a day is relatively much more likely to die from CHD within the next decade than a non-smoking woman of same age with a normal cholesterol level.

But the absolute likelihood of his dying during this time is still small (high relative risk, low absolute risk).

Even though a number of environmental factors have been implicated in the development of HT, salt intake has received the greatest attention.

Even this factor illustrates the heterogeneous nature of the hypertensive population, in that the BP in only 60 per cent of hypertensives is responsible to the level of sodium intake.

The cause of this special sensitivity to salt varies. In about half the patients, there is some primary pathology which accounts for the salt sensitivity.

In the remainder, the pathophysiology is still uncertain but postulated contributing factors include chloride intake, calcium intake, a generalised cellular membrane defect, insulin resistance and `non modulation' to rennin ( a hormone secreted by kidneys).

Most studies assessing the role of salt in HT have assumed that it is the sodium ion that is important. However, some investigators have suggested that the chloride ion may be equally important.

This is based on the observation that feeding chloride free sodium salts to salt-sensitive hypertensive animals fails to increase arterial pressure. A low calcium intake has also been associated with an increase in blood pressure in epidemiological studies.

Since there is no easy test to distinguish salt responsive from salt resistant humans, the current emphasis on decreasing sodium intake in all humans makes some sense.

However, the degree to which HT can be ameliorated or prevented (HT is a non-curable disease) will obviously vary with the salt sensitivity of the individual.

Previously patients were instructed to curtail sodium intake drastically. But now investigators have suggested that this is not necessary. They base their conclusion on studies, which have documented that, mild sodium restriction significantly potentiates the efficacy of nearly all antihypertensive drugs.

Thus, by making it possible to control blood pressure with lower doses of drugs, sodium restriction leads to a reduction in side effects. In addition, it is quite proved that the level of sodium intake does influence the blood pressure.

Source : The Hindu